The method to produce oxygen from oxygen concentrators using pressure swing adsorption is widely known in the art, see Spearman et al., U.S. Pat. No. 7,331,342 and McCombs et al., U.S. Pat. No. 6,558,451. Oxygen concentrators produce a high level of oxygen of approximately 95% at flow rates approximately 1-10 liters per minute (lpm). There are approximately 2 million oxygen concentrators in use in America.
Oxygen concentrators that utilize pressure swing adsorption to increase the oxygen concentration cause the moisture level to be very low. In fact, the oxygen can be so dry to a patient that the patient can suffer bloody noses and dry lungs due to the rapid evaporation of fluid from tissue cells within the nasal passage way and lungs. To combat the problem of dry gas being delivered to the patient, health care providers will do one of two things to deliver humidified gases to their patients, each of which has shortcomings.
One technique to humidify the oxygen is to connect the patient oxygen port outside of the concentrator to a water bubbler through which the oxygen bubbles and adsorbs water that is subsequently delivered to the patient at relatively high levels of humidity, approximately 50%-90%. This high level of humidity is beneficial to the patient and provides comfort to the patient.
Bacteria however, can grow within the humidifier itself, thereby jeopardizing the patient's safety. Additionally, the bubblers on a humidifier are recommended to be changed quite frequently by the health care provider. These bubblers are not reimbursed and are paid for out of the health care provider's pocket. This can be quite costly for a healthcare provider.
Another technique to provide humidification is through membrane gas humidifiers. Porous Media's HUMIDIFLOW membrane gas humidifier, which was the subject of U.S. Pat. No. 7,331,342, provides humidification to the patient without using water bubblers, but rather using a hollow fiber membrane having a high selectivity of water over nitrogen and oxygen.
This device is installed on the upstream side of the air compressor in the oxygen concentrator and plumbed to flow atmospheric air from the air compressor across one side of the membranes and oxygen from the downstream side of the molecular sieve beds across the other side to induce a gradient such that the water vapor in the atmosphere on the one side of the fibers transfers to the dry oxygen on the other side of said hollow fiber membrane to a level of humidity that is close to that of the room air.
Porous Media teaches installing the HUMIDIFLOW membrane gas humidifier inside the oxygen concentrator: “In one embodiment of the present invention, the membrane device is installed in the oxygen concentrator such that the membrane device engages a stream of ambient air prior to the compression of the ambient air by a compressor while an oxygen-enriched gas engages the membrane device after the oxygen-enriched gas has engaged a regulator and needle valve.”
“In an alternative embodiment of the present invention, the membrane device is installed in an oxygen concentrator such that the membrane device engages the stream of ambient air after compression of the ambient air by the compressor while the oxygen-enriched gas engages the membrane device prior to the engagement of the oxygen-enriched gas with the gas regulator” and “More specifically, since membrane devices used in oxygen concentrators are usually installed downstream of the compressor”, and “A second embodiment of the present invention involves installing the membrane device in an oxygen concentrator . . . ” from page 3 of the provisional patent.
There are many problems with the prior art inventions created by having to install the device in the inside of an oxygen concentrator. As illustrated from an instructional installation DVD for the HUMIDIFLOW membrane gas humidifier, which was purchased from a publicly available distributor of Porous Media listed on the HUMIDIFLOW website (The Aftermarket Group, OH) the following problems can be observed pertaining to the installation of the HUMIDIFLOW membrane gas humidifier. First is that the health care provider is required to remove the oxygen concentrator cabinet that is generally secured by screws to a frame on the oxygen concentrator.
Then the health care provider is required to re-plumb the original manufacturer's equipment so that the oxygen tubing is re-routed from the flow meter to the membrane and from the membrane back to the patient. Next, the health care provider must ensure that the membrane is secured to the inside of the concentrator using nylon zip ties that may come loose during transportation or if not installed properly, cause potential rattling of the membrane against other components inside of the concentrator.
In one case, the health care provider is instructed to install a custom compressor inlet filter to the inlet of the HUMIDIFLOW membrane gas humidifier. The intake filter of the HUMIDIFLOW membrane gas humidifier kits may become detached from the module and fall onto the compressor cooling fan during patient treatment. If the filter were to come in contact with the fan blades this could stop the fan from operating and cause the concentrator to overheat and interrupt the flow of oxygen to the patient.
Further, there are dozens of oxygen concentrator brands and part numbers on the market, each oxygen concentrator brand requiring a HUMIDIFLOW membrane gas humidifier with different tubing lengths and various connectors. One HUMIDIFLOW membrane gas humidifier requires a special mounting bracket that one has to mount to the top of the air compressor to secure the HUMIDIFLOW membrane gas humidifier in place.
This process requires removing a portion of the air compressor OEM's air compressor components to retrofit a particular oxygen concentrator for the HUMIDIFLOW membrane gas humidifier. As one can see, the installation of the HUMIDIFLOW membrane gas humidifier is less than ideal from an operations stand point or ease of use from the patient's perspective.
It is common for an oxygen concentrator dealer to carry multiple brands of oxygen concentrators and if this is the case, the dealer must inventory as many part numbers of HUMIDIFLOW membrane gas humidifiers as there are concentrators. It is conceivable that the healthcare provider would have to inventory up to 15 or more different HUMIDIFLOW membrane gas humidifier part numbers.
Every oxygen concentrator on the market requires that the health care provider measure and verify the oxygen concentration performance of the concentrator. This process is generally done with an oxygen sensor and can be easily measured by holding the sensor up to the oxygen flow meter. However, the oxygen sensors will only give an accurate reading of the concentrator's oxygen level output in the presence of dry gas.
Since the prior art must be installed to verify that it is not affecting the oxygen levels, one must now take another step to dry the gas that has been humidified by the membrane. The way this process is accomplished is by purchasing another in line air dryer comprised generally of PVC tubing and a desiccant.
The operator must install the in line dryer at the concentrator's outlet, dry the oxygen using the desiccant dryer and then measure the oxygen concentration of the concentrator. This desiccant dryer can have a very short life and must be either re-charged by putting in an oven, or the operator must purchase another in line dryer.
While membrane devices such as the Teijin and HUMIDIFLOW membrane gas humidifier address a need in the marketplace to provide comfortable levels of humidity without requiring liquid water when the ambient humidity is at levels of 25-30% RH, there exists an inherent problem with prior art membranes in their ability to control humidity to the patient in dry weather. As explained in the Teijin patent, the “make up” air is the ambient air that is drawn through the air compressor.
The oxygen is plumbed to the Teijin membrane humidifier and picks up the moisture from the “make up” air side of the membrane via diffusion across the membrane. If the room air is 15% RH, for example in the case of many Southwestern states in the winter months, supplemental humidification may be needed. To provide higher levels of humidity to the patient when the room RH is low, the humidifier may need to be installed near the oxygen concentrator.
To increase the humidity to the patient in dry weather, one must increase the humidity in the room at the inlet of the air compressor or “make up air” as Teijin refers to this process, using water droplets and water vapor from a room air humidifier. Most compressors installed in oxygen concentrators operate at approximately 100 lpm. Most oxygen concentrators such as Teijin's have an oxygen flow rate of approximately 5 lpm.
Both of the Teijin and Porous Media membrane humidifiers require the plumbing of the oxygen line to a port of the membrane. Both Teijin and the HUMIDIFLOW offer the use of a fan inside the oxygen concentrator to direct the airflow across the membrane.
Another membrane humidifier very similar to the Porous Media HUMIDIFLOW is mentioned in the Teijin patent. The oxygen flows on the opposite side of the fibers containing the makeup air. When a supplemental room air humidifier is installed near the inlet of one of these common membrane humidifiers, the small flow of oxygen relative to the makeup air becomes saturated with water and is delivered to the patient.
This is good for the patient because much of the oxygen will now be saturated. However, In the case of a conventional membrane such as the above mentioned membranes, much of the compressed air will also be saturated, but now entering the molecular sieve beds due to the fact that only a relatively small amount of water will be removed from the makeup air and put into the oxygen stream. This deficiency in these conventional membranes will lead to reduced sieve life.
While the above mentioned membranes are generally effective at increasing the humidity in dry weather to more comfortable levels of approximately 30% RH using a room air humidifier, for the prior art membranes to provide much more humidity than this is extremely difficult without encountering major problems for the oxygen concentrator as well as the patient's home.
In the average US household, each furnace is equipped with a blower ranging from several hundred SCFM to several thousand SCFM. This means that the air exchange in a standard 10 foot×10 foot room can be 50-200 SCFM. To compound the problem, the atmospheric air drawn by the compressor is rushing through the Teijin and HUMIDIFLOW membranes at a rate of approximately 100 lpm from the air compressor compared to the relatively small flow of 5-10 lpm for the dry oxygen plumbed on the opposite side of the fibers.
The average room air supplemental humidifier patients purchase at pharmacies and drug stores only put out several liters per minute to several SCFM of saturated humidity, which is obviously not enough to keep up with the air compressor inlet flow rate and the air exchange of the room.
This means in order to humidify a 10 foot×10 foot room to levels of high humidity over about 50%, preferably >60-80% one would literally have to line the floors of this room with humidifiers which in turn would coat every square inch of surface area of the room, including the flooring, walls, windows, books, electrical fixtures, etc. with water droplets, ultimately resulting in the growth of mold and spores.
As indicated before, the effects of this amount of water on the oxygen concentrator would be overwhelming to the sieve beds and would cause a substantial reduction in sieve life, not to mention rusting the metal and electrical components within the concentrator.
The Teijin oxygen concentrator which is subject of U.S. Pat. No. 6,669,956 utilizes a similar operational principal of the Porous Media oxygen concentrator, however it features a NAFION cationic conductive membrane that is coupled to a cathode and an anode. When an electric current is applied to the conductive membrane, it produces a higher level of humidity on the patient outlet end than the atmospheric air or “make up” air as Teijin describes it. This membrane however loses its charge over time and becomes a “passive” membrane just like the Porous Media HUMIDIFLOW membrane gas humidifier.
Teijin describes another Japanese membrane that basically accomplishes a similar “passive” humidification means as the membrane gas humidifier in JP Patent No. 2-99113. The indicated benefit of the Teijin design is that for a period of time (albeit very brief), they are able to control the level of humidity to the patient through the use of applying a higher or lower amount of current to their conductive membrane, depending upon the amount of humidity desired at the patient end.
The Burioka oxygen concentrator connects a polyimide hollow fiber (from UBE Industries, Ltd, Japan) membrane shell consisting of 4 connection ports to an air compressor and an oxygen source as described in an article entitled “Efficacy of a Newly Developed Pressure Swing Adsorption Type Oxygen Concentrator with Membrane Humidifier: Comparison with Conventional Oxygen Concentrator with Bubble Water Humidifier.”
The air compressor takes compressed air and compresses the atmospheric air to between about 14 psig and 28 psig. The paper shows a chart illustrating that at approximately 20% RH room air humidity. Burioka was able to achieve 50-60% RH in the patient gas and approximately 80% RH in the patient gas when the room was 30% RH.
However, the Burioka prototype suffers from several design deficiencies. First is that the membrane must be installed downstream of an air compressor, which is inside the oxygen concentrator. This configuration would be extremely difficult for aftermarket installations.
Since some oxygen concentrator air compressors can operate at relatively high temperatures inside the cabinet (nearly 230° F. in some cases) and the compressors can put out an extremely high amount of contamination, this configuration would expose the membrane to conditions of operation that could cause fatigue and contamination of the membranes.
Further, the Burioka design of humidification system provides the patient and the health care provider with a level of humidification that could be too high when operated continually at higher levels of room RH and leaves the patient with no choice or control over the level of humidity.
U.S. Pat. No. 7,331,342 indicates that humidity in the Burioka product is provided at a higher level than the atmospheric air and mentions two techniques to overcome over humidification by the membrane devices. First, the membrane devices can be used in an environment where the ambient humidity never exceeds an amount that would cause the oxygen-enriched gas to become over humidified. However, since many of these devices are used in a patient's home under a variety of environmental conditions, the ambient humidity is difficult to control.
Second, a shunt can be installed so that a portion of the oxygen-enriched gas bypasses the membrane device, and remains at an extremely low humidity. When the streams of oxygen-enriched gas are later remixed, an optimal humidity can be achieved. This system however, requires adjustment by the user to match ambient conditions as well as requiring additional valves and tubing.
Porous Media teaches against being able to control the humidity of the patient gas with the use of the HUMIDIFLOW membrane gas humidifier, and teaches that it is not possible to create higher levels of humidity on the outlet of the HUMIDIFLOW membrane gas humidifier than the atmospheric air, their concern being condensation or “rain out.” Porous Media views condensation as harmful: “However, if the oxygen-enriched air stream exiting membrane device 63 were allowed to cool to ambient temperature to enable a patient to breathe the oxygen-enriched air, harmful condensation can occur.”
The Spearman patent indicates that: “FIG. 4 shows an embodiment of the oxygen concentrator 92 of the present invention. Oxygen concentrator 92 uses a membrane device 63 similar to the membrane device shown in FIG. 2, but with the first inlet 44 of the membrane device 63 in fluid communication with the outlet 39 of the inlet filter 37 and the first outlet 45 of the membrane device 63 in fluid communication with the inlet 41 of the compressor 40.”
Thus, the same stream of air is passed through the membrane device 63 from the first inlet 44 to the first outlet 45 as shown in FIG. 2, but the stream of air is now at approximately ambient pressure and thus at nominally the same pressure as the oxygen-enriched gas passing from the second inlet 61 to the second outlet 62 of the membrane device 63.
This means that the partial pressure of water in the oxygen-enriched gas exiting at the second outlet 62 of the membrane device 63 should be no greater than the partial pressure of water in the air entering the membrane device 63 at the first inlet 44 of the membrane device 63 and thus no greater than the ambient partial pressure of water. As a result, as the oxygen-enriched gas cools on the way to the patient, condensation is inhibited or eliminated.
Thus, there is no need of a bypass valve as in FIG. 2. Additionally, the Patent Examiner from US application Ser. No. 10/958,973 reaffirmed that the “invention requires equal pressure at both level of humidification of gas to overcome condensation of gas at the second level of humidification gas . . . ” The provisional patent states “In one embodiment . . . unlike devices in the previous art, the pressure of both the air and the oxygen enriched air streams will be nominally equal to the environmental pressure and thus each other.”
From the provisional patent page 3, Porous Media describes the following installation scenarios in which the pressures of oxygen gas and the feed gas are the same: “In this second embodiment the outlet of the compressor is in fluid communication with the inlet of side one of the membrane in the membrane device. The outlet of side one of said membrane device is in fluid communication with the inlet of the oxygen concentration system, which consists of a valve system, adsorption beds, and usually a buffer tank. The outlet of said oxygen concentration system is in fluid communication with side two of the membrane in said membrane device.
The outlet of side two of said membrane device is in fluid communication with, in seriatim, the gas pressure regulator, the flow control valve, and the patient. In this second embodiment both the air and the oxygen-enriched stream are at nominally the same pressure which is higher than the ambient pressure. Like the first embodiment, this second embodiment is different from prior art since there is no total pressure gradient across the membrane.”
Porous Media establishes the difference between their device that operates at equal pressures and the Burioka device which is at unequal pressures. Further, Porous Media illustrates the importance of their invention operating at equal pressures and teaches away from pressure gradients: “It is sometimes thought by those experienced in the art that a total pressure gradient across the membrane is required to produce flux across the membrane, suggesting that the module would need to be installed as in FIG. 2 to function, but this is not the case. Since flux across the membrane is caused by a partial pressure gradient of a compound in the respective streams, and the oxygen enriched air enters the membrane device 8 at entrance 10 extremely dry, there is still a partial pressure gradient of water to drive the membrane flux even though the total pressure on the 2 sides of the membrane is nominally equal.”
Porous Media indicates in the patent “no matter how the membrane is designed, or how large it is, or how permeable the membrane is to water vapor, the partial pressure of water in the exiting oxygen enriched stream can never be greater than the partial pressure of water in the entering air stream” (to the compressor that is).